1. Field of the Invention
The present invention relates to a homogeneous catalyst based on titanium, its preparation and its use in the copolymerization of α-olefins and in the preparation of terpolymers of α-olefins with non-conjugated dienes.
The present invention also relates to a catalytic system comprising a titanium complex, a reducing/chlorinating agent based on a chlorinated aluminum alkyl and a cocatalyst based on aluminum trialkyl.
Finally the present invention relates to a process for the co- and ter-polymerization of α-olefins with non-conjugated dienes in the presence of said catalytic system.
2. Description of the Related Art
Ethylene-propylene (EPR) copolymers and the corresponding terpolymers with non-conjugated dienes (EPDM) are important elastomers and are industrially produced with catalysts based on vanadium such as VCl4, VOCl3, and V(AcAc)3 which are soluble in many hydrocarbon solvents. Although these catalysts produce a highly random ethylene-propylene copolymer (rE×rp<1), their activities are greatly influenced by the temperature. This phenomenon is drastic and prevents their use at high temperatures. Furthermore, as is well known, the residues of these catalytic systems are toxic and tend to give the resulting polymers undesired colouring.
In this respect, heterogeneous titanium-based catalysts have been widely studied for the polymerization of ethylene or propylene, together with the methods for the preparation of these catalysts. Co-crystallized titanium (III) compounds have been prepared (TiCl3×1/3 AlCl3) for the reduction of TiCl4 either with metallic aluminum or with organometallic derivatives of aluminum. TiCl3 without AlCl3 has also been prepared for the reduction of TiCl4, with hydrogen, at temperatures of 800° C. Titanium catalysts supported on MgCl2 or SiO2 have also been prepared. The above catalysts based on TiCl3 have an extremely high activity for the homopolymerization of ethylene and propylene but show a low activity compared with vanadium for the random copolymerization of these olefins. Heterogeneous titanium catalysts are therefore capable of copolymerizing ethylene with α-olefins such as propylene but only with low activities. The copolymers obtained, moreover, have partially isotactic propylene sequences with product values of the relative reactivities rE×rp>5; this result is reflected in block-type polymers, with crystalline domains, also due to long ethylene sequences and consequently not of the elastomeric type. These catalysts are also inactive towards the entrance of a possible diene termonomer.